Process of preparation of titanium



PRCESS F PREPARATION UF TITANIUM Werner C. Muller, Roslyn, N. Y., assigner to Nationai Distillers and Chemical Corporation, a corporation of Virginia Application August 17, 1955, Serial No. 529,059

2 Claims. (Cl. 75-84.5)

This invention relates to an improvement in a process and apparatus for making massive titanium metal sponge by reduction of a titanium chloride with sodium and, more particularly, to a process and apparatus for controlled and consistent formation of titanium sponge devoid or substantially devoid of unreduced titanium chlorides or subchlorides or unreacted sodium metal and from which titanium metal of improved ductility characteris tics may be obtained.

1n recently developed and improved sodium reduction processes, the steps of reduction of the chloride followed by heat soaking to produce massive titanium metal are separated, thereby permitting each to be carried out in a more efficient manner. The first or chemical reduction step is preferably operated continuously. In actual operation, both sodium and titanium tetrachloride are added continuously or semi-continuously into a reactor containing preformed finely divided products of the reaction and in which additional products are continuously or semi-continuously formed therein:

As the indicated product mixture forms, it is continuously or semi-continuously withdrawn from the reduction vessel. This mixture contains approximately the theoretical percentage of Ti mixed with salt-i. e., Tir4NaCl. The temperature of the reduction step may be from 150 C. up to 600 C. or higher as long as a finely divided solid reaction mixture consisting of finely divided solid sodium chloride admixed with finely divided solid titanium is produced which can be readily stirred by mechanical agitation with conventional type stirrers and can be handled by conventional means.

This reaction mixture may be cooled and sto-red for future processing, or preferably it may be immediately transported by means of a screw or other convenient conveying device to a heat soaking vessel which is the second or sponge formation zone. Operating in two steps, the heat of reaction is liberated at a relatively low temperature level where materials of construction are a very slight problemi and the reduction process can be substantially continuous and is therefore susceptible to rigorous controls.

lt has been discovered that the sponge growing process which occurs during the heat soaking or sintering step is rapid once the sodium chloride in the Ti:4NaCl powder has become molten. It has also been discovered that by operating in a manner described hereinafter titanium sponge can be obtained from which metallurgical titanium of consistent improved ductility characteristics is produced.

Actual experiments have indicated that in certain instances the exact amount of molar excess of sodium present during the soaking operation is critical and requires rigid control. Thus, for example, in certain instances wherein a substantial deficiency of sodium ispresent in the soaking vessel during the heating period. the reducn 65,738 Patented Dec. 23, 1958 tion to titanium metal may be incomplete and titanium subchlorides may remain in the finished sponge causing the formation of titanium oxides during subsequent leaching operations with ultimate production of titanium metal of unsatisfactory ductility characteristics. In certain other instances wherein a substantial excess of sodium is present during the soaking operation, it may remain in the vicinity of the finished sponge and react with water during subsequent leaching operations, causing the release of hydrogen and heat, raising the temperature of the sponge and leading to reaction of titanium metal with the leaching water. These conditions likewise lead to production of a sponge from which titanium metal of unsatisfactory ductility properties is produced.

It is difiicult to measure the titanium tetrachloride and sodium reactants with suiiicient accuracy to assure a constantly correct and critical stoichiometric balance for production of a sponge from which titanium metal of improved ductility properties is produced. It thus becomes necessary to employ a measurement to indicate when scdium is in correct stoichiometric balance for a particular soaking operation and thereby control it and the properties of the final product. This invention describes a method and an apparatus useful therefore, to control the concentration of sodium in the molten salt phase of the heat soaking reaction vessel by controlling the partial pressure of sodium vapor above the molten salt mass. Operating thus, if a supply of sodium is maintained at a controlled temperature in the coolest section in the vapor phase of the reaction vessel, the vapor pressure of the sodium so maintained is equal to the partial pressure eX- erted by the sodium in the molten salt phase. For example, and in instances wherein titanium metal of improved ductility characteristics may require that the sodium be present during the soaking operation in a concentration on the order of magnitude of about 0.01 up to 5 weight percent over the stoichiometric quantity, theoretically required to reduce any titanium chlorides that are present to titanium metal, the partial pressure exerted by the sodium in the molten salt would accordingly be in order of magnitude of l to 35 mm. Sodium exerts a vapor pressure of 7.5 mm. at approximately 534 C.

TABLE I 1% (by weight) 2% (by Weight) 5% (by Weight) (Soaking Excess Sodium Excess Sodium Excess Sodium Temp.) Temp. TiNaCl Partial Temp. Partial Temp. Partial Temp. Mixture, C. Pressure Sodium Pressure Sodium Pressure Sodium Sodium, Receiv- Sodium, Receiv- Sodium, Receiv mm. er, C. mm. er, c C. mm. er, C.

In order to illustrate an embodiment for practice oi this invention, a soaking vessel is provided which is essentially completely submerged in a heating zone and has a vapor space extending above the heating zone and means disposed in said vapor space for control of the partial pressure of sodium vapor in the vapor space and control of the amount of sodium present at all times in the Ti-NaCl mass. Generally, only a water wash is required to remove the sodium ions and chloride ions finally present in the sponge as salt, the chief by-product of the reduction reaction of sodium 4metal on titanium tetrachloride. This avoids the necessity of employing an acid wash for the final sponge.

In order to form high quality titanium sponge rapidly and efficiently during the heat soaking step, a sufiicient period of time must be provided in which the temperature 'I A is held in the range of 850 tol150"C.,"which isthe` critical temperature range above the melting point of the lay-product sodium chloride. The period of time necessary is dependent on the exactisize of the charge and on its physical and chemical nature but will generally vary between 12 and 36 hours. Suicient time must be allowed during this period to permit the complete reduction of traces of any unchanged titanium sub-halides in the presence of the sodium, since such sub-halides as titanium dichloride and titanium trichloride interfere seriously with the quality of the resultant titanium sponge. It is during this period of the process that the control over the concentration of sodium is exercised. If desired, just prior to final recovery of the titanium metal, the temperature of the sodium receiver may be reduced somewhat to effect the distillation of any excess sodium and hasten the final stages of sponge structure development. However, this feature is not necessary for production of high quality sponge.

I Operating in this manner, a sponge is produced from which residual salt can easily and quickly be lleached without harmful effects on properties of the titanium. If desired, mild agitation of the Tiz4NaCl mixture while it is in the temperature range of 800 to 1150 C., immediately after the major portion of the by-product salt has become molten, causes the spongen to collect very rapidly into a more dense mass, containing less sodium chloride. During the heat soaking step, the forming titanium sponge mass contracts or shrinks from the Walls of the sintering vessel. If the sponge is properly treated and the sintering step properly controlled, high quality titanium sponge can be produced with only water washing, no acid treatment being necessary.

Both reaction vessels are maintained free of oxygen at all times and are preferably blanketed at all times with an inert gas. The presence of nitrogen and the nitrides resulting therefrom adversely `affects the titanium metal produced and the use of this gas is therefore to be avoided. It is preferred to use such inert gases as the rare gases and, of special importance for commercial use, are argon and helium. If desired, the sodium employed is stored and used under the same protective blanket.

As to the apparatus aspects of this invention; it cornprises a closed vessel adapted for heating a mass comprising a mixture of tinely divided titanium metal and sodium chloride to a temperature suitable for carrying out the soaking operation, said vessel having means providing a vapor space in open communication with and above said mass, and collecting means disposed in said vapor space and adapted to control the temperature of material in said collecting means. More specifically, the apparatus embodied herein comprises a closed vessel having a neck-like portion adapted to provide a vapor space in open communication with .and above a mass of material charged to said vessel, means for heating material charged to said vessel, and a trough-like means disposed in said neck-like portion, said trough-like means being in indirect heat exchange relationship with a temperature control medum whereby material in said collecting means is subjected to temperature control. More specific details of apparatus suitable for practice of this invention are set forth in the description of the embodiment shown in the drawing and its use in carrying out the invention. Y

The following examples will further serve to illustrate the invention although it is not intended to limit the in vention specifically thereto.

Example ing vessel 2 to which cover and vapor chamber 3 have been attached. Before charging, the-vessel is evacuated and filled with an inert atmosphere to avoid contamination from moisture, oxygen, nitrogen or the like. The charged vessel is submerged in heating medium 4 which is heated to elevated temperature thereby causing salt in the mixture 1 to fuse. -The mixture of fused salt and titaniumis maintained at a temperature in the range of 850 to 1150 C. for a period of 12 to 30 hours. At this temperature, the finely divided titanium particles in the sintering vesselmigrate through the molten salt mixture to form a ductile titanium sponge. Sodium metal dissolved in the salt mixture exerts a partial pressure of sodium vapor above the salt mixture, causing sodium vapor to migrate to the upper zone of vapor space 3. In the upper zone of the vapor space, chamber 5 is provided to trap liquid sodium condensed by a suitable heat transfer medium circulated through jacket 6 surrounding chamber 5. .Insulation 7A is provided surrounding jacket 6 to permit the maintenance of a temperature differential between chamber 5 and heating medium 4. The heat transfer medium to chamber 6 isV admitted through pipe 8 controlled by valve 9 and removed through pipe 10 controlled by valve 11. The temperature of the heat transfer medium is regulated to maintain the temperature of chamber 5 from 400 to 600 C. By proper selection Vand control of the temperature maintained in chamber 5,

sodium can be caused to migrate from salt titanium mixture l to chamber 5 or from chamber 5 to salt mixture 1, as required to maintain the appropriate concentration of sodium in salt mixture 1. Inert gas is permitted to flow to or from the vessel through pipe 12 controlled b y valve 13, to maintain the desired pressure within sintering vessel 2.

In a typical operation, titanium-salt mixture 1 is'maintained at a temperature of 950 centigrade. At this temperaturev an excess of sodium concentration of one-half of one percent exerts a partial pressure of sodium vapor of 1.29 mm. With the cooling medium in jacket 6 at` 455 C., any sodium in excess of 1.29 mm. will condense and be trapped in chamber 5 thus maintaining the desired one-half of one percent sodium concentration in the molten salt mixture. If the sodium concentration in salt mixture 1 is less than one-half of one percent, the partial pressure of sodium vapor in vapor space 3 will be less than 1.29 mm., and liquid sodium in chamber 5 will vaporize to increase the partial pressure of sodium vapor in vapor space 3 to 1.29 mm. At the higher partial pressure of sodium in vapor space 3 sodium will condense in salt mixture 1 to increase the concentration of sodium in the salt mixture to the desired concentration of onehalf of one percent.

In carrying out the invention, the desired amount of sodium in the mixture to be subjected to the soaking operation may be provided in the mixture prior to start of the operation or, if desired, sodium may be placed in the collecting means whereby, by means of the temperature control by the heat exchange medium in jacket 6, sufficient sodium will be vaporized so as to provide in the vapor space a partial pressure such as that exerted by the desired excess of sodium metal in the mixture undergoing treatment in the soaking operation.

-While there are above disclosed but a limited number of embodiments of the invention herein presented, it is possible to produce still other embodiments without departing from the inventive concept herein disclosed, and it is desired therefore that only such limitations be iinposed on the appended claims as are stated therein.

What is claimed is:

1. In a process for preparation of a titanium sponge by treatment at a temperature of about 850 to about 1150 C. in an inert atmosphere and for a time sufficient for complete reduction to titanium metal of a mixture comprising nely divided titanium metal and sodium chloride in the presence of sodium metal in excess of that theoretically required to reduce titanium chlorides in said mixture to titanium metal, said mixture having been prepared by reduction of titanium chloride by sodium, the improvement which comprises maintaining a vapor zone above the mixture undergoing said treatment and in which vapor space a partial pressure is exerted by migration of sodium vapor from dissolved sodium metal in said mixture, and controlling the sodium metal in said mixture to the desired concentration by controlling the partial pressure exerted by said sodium vapor in said vapor zone to a vapor pressure such as that exerted by the desired concentration of sodium in said mixture by positioning a collecting zone in said vapor phase, said collecting zone being maintained under such temperature conditions so that sodium vapors condense in said collecting means when the vapor pressure exerted by the sodium vapor in said vapor space is higher than the vapor pressure exerted by the desired concentration of sodium in said mixture and said condensed sodium in said collecting zone vaporizes when said mixture contains a deciency of sodium to provide in said vapor space a partial pressure such as that exerted by the desired concentration of sodium in said mixture.

2. The process of claim 1 wherein said treatment is carried out for a period of about 12 to 36 hours.

References Cited in the file of this patent UNITED STATES PATENTS 2,148,345 Freudenberg Feb. 2l, 1939 2,546,320 Rostron Mar. 27, 1951 2,564,337 Maddex Aug. 14, 1951 2,607,674 Winter Aug. 19, 1952 2,621,121 Winter Dec. 9, 1952 2,663,634 Stoddard et al Dec. 22, 1953 2,703,752 Glasser et al. Mar. 8, 1955 2,707,679 Lilliendahl et al May 3, 1955 2,753,256 Olson July 3, 1956 FOREIGN PATENTS 675,933 Great'Britain L Q July 16, 1952 152,033 Australia June 24, 1953 717,930 Great Britain Nov. 3, 1954 720,517 Great Britain Dec. 22, 1954 720,543 Great Britain Dec. 22, 1954 

1. IN A PROCESS FOR PREPARATION OF A TITANIUM SPONGE BY TREATMENT AT A TEMPERATURE OF ABOUT 850* TO ABOUT 1150*C. IN AN INERT ATMOSPHERE AND FOR A TIME SUFFICIENT FOR COMPLETE REDUCTION TO TITANIUM METAL OF A MIXTURE COMPRISING FINELY DIVIDED TITANIUM METAL OF A MIXTURE COMPRISING FINELY DIVIDED TATANIUM METAL AND SODIUM CHLORIDE IN THE PRESENCE OF SODIUM METAL IN EXCESS RIDES IN SAID MIXTURE TO TITANIUM METAL, SAID MIXTURE HAVING BEEN PREPARED BY REDUCTION OF TITANIUM CHLORIDE BY SODIUM, THE IMPROVEMENT WHICH COMPRISES MAINTAINING A VAPOR ZONE ABOVE THE MIXTURE UNDERGOING SAID TREATMENT AND IN WHICH VAPOR SPACE A PARTIAL PRESSURE IS EXERTED BY MIGRATION OF SODIUM VAPOR FROM DISSOLVED SODIUM METAL IN SAID MIXTURE, AND CONTROLLING THE SODIUM METAL IN SAID MIXTURE TO THE DESIRED CONCENTRATION BY CONTROLLING THE PARTIAL PRESSURE EXERTED BY SAID SODIUM VAPOR IN SAID VAPOR ZONE TO A VAPOR PRESURE SUCH AS THAT EXERTED BY THE DESIRED CONCENTRATION OF SODIUM IN SAID MIXTURE BY POSITIONING A COLLECTING ZONE IN SAID VAPOR PHASE, SAID COLLECTING ZONE BEING MAINTAINED UNDER SUCH TEMPERATURE CONDITIONS SO THAT SODIUM VAPORS CONDENSE IN SAID COLLECTING MEANS WHEN THE VAPOR PRESSURE EXERTED BY THE SODIUM VAPOR IN SAID VAPOR SPACE IS HIGHER THAN THE VAPOR PRESSURE EXERTED BY THE DESIRED CONCENTRATION OF SODIUM IN SAID MIXTURE AND SAID CONDENSED SODIUM IN SAID COLLECTING ZONE VAPORIZES WHEN SAID MIXTURE CONTAINS A DEFICIENCY OF SODIUM TO PROVIDEE IN SAID VAPOR SPACE A PARTIAL PRESSURE SUCH AS THAT EXERTED BY THE DESIRED CONCENTRATION OF SODIUM IN SAID MIXTURE. 